The human heart, and generally all mammalian hearts, comprises two blood pumps that operate in synchrony to oxygenate and deliver oxygenated blood to the body. A first pump receives deoxygenated blood after it has coursed through blood vessels in the circulatory system to deliver oxygen and nutrients to the various parts the body, and pumps the deoxygenated blood through the lungs to be oxygenated. The second pump receives the oxygenated blood from the lungs and pumps it to flow through the blood vessels of the circulatory system and deliver oxygen and nutrients to the body parts. The two pumps are located adjacent each other in the heart and each pump comprises two chambers, an atrium that receives blood and a ventricle that pumps blood.
The first pump, which receives deoxygenated blood to be pumped to the lungs, is located on the right side of the heart and its atrium and ventricle are accordingly referred to as the right atrium and right ventricle. The second pump, which receives oxygenated blood to be pumped to the body, is located on the left side of the heart and its atrium and ventricle are referred to as the left atrium and left ventricle of the heart. The right and left atria are separated by a wall in the heart referred to as the interatrial septum and the right and left ventricles are separated by a wall in the heart referred to as the interventricular septum.
Deoxygenated blood enters the right atrium via blood vessels referred to as the superior vena cava and inferior vena cava. During a part of the heart cycle referred to as diastole the right ventricle is relaxed and the deoxygenated blood in the right atrium flows from the right atrium into the right ventricle via a valve, referred to as a tricuspid valve, which connects the right atrium to the right ventricle. The right ventricle contracts during a part of the heart cycle referred to as systole, to pump the deoxygenated blood that it receives from the right atrium out of the ventricle and into the pulmonary artery via a valve referred to as the pulmonary valve. The pulmonary valve interfaces the pulmonary artery with the right ventricle. The pulmonary artery delivers the deoxygenated blood to the lungs for oxygenation. The tricuspid and pulmonary valves control direction of blood flow in the right side of the heart. The tricuspid valve opens to let deoxygenated blood flow from the right atrium into the right ventricle and closes to prevent deoxygenated blood from regurgitating into the right atrium when the right ventricle contracts. The pulmonary valve opens to let blood enter the pulmonary artery when the right ventricle contracts and closes to prevent blood regurgitating into the right ventricle when the right ventricle relaxes to receive blood from the right atrium.
The left atrium receives oxygenated blood from the lungs via pulmonary veins. Oxygenated blood flows from the left atrium into the left ventricle during diastole via a bicuspid valve referred to as the mitral valve, which opens during diastole to allow blood flow from the left atrium to the left ventricle. The left ventricle contracts during systole to pump the oxygenated blood that it receives from the left atrium out of the heart through the aortic valve and into the aorta, for delivery to the body. The mitral valve operates to prevent regurgitation of oxygenated blood from the left ventricle to the left atrium when the left ventricle contracts to pump oxygenated blood into the aorta. The aortic valve closes to prevent blood from regurgitating into the left ventricle when the left ventricle relaxes to receive blood from the left atrium.
Each valve comprises a set of matching “flaps”, also referred to as “leaflets” or “cusps”. that are mounted to and extend from a supporting structure of fibrous tissue. The supporting structure has a shape reminiscent of an annulus and is often conventionally referred to as the annulus of the valve. The leaflets are configured to align and overlap each other, or coapt, along free edges of the leaflets to close the valve. The valve opens when the leaflets are pushed away from each other and their free edges part. The aortic, pulmonary, and tricuspid valves comprise three leaflets. The mitral valve comprises two leaflets.
The leaflets in a valve open and close in response to a gradient in blood pressure across the valve generated by a difference between blood pressure on opposite sides of the valve. When the gradient is negative in a “downstream flow” or antegrade direction, in which the valve is intended to enable blood flow, the leaflets are pushed apart in the downstream, antegrade direction by the pressure gradient and the valve opens. When the gradient is positive in the downstream direction, the leaflets are pushed together in the upstream or retrograde direction so that their respective edges meet to align and coapt, and the valve closes.
For example, the leaflets in the mitral valve are pushed apart during diastole to open the mitral valve and allow blood flow from the left atrium into the left ventricle when pressure in the left atrium is greater than pressure in the left ventricle. The leaflets in the mitral valve are pushed together so that their edges coapt to close the valve during systole when pressure in the left ventricle is greater than pressure in the left atrium to prevent regurgitation of blood into the left atrium.
Each valve is configured to prevent misalignment or prolapse of its leaflets as a result of positive pressure gradients pushing the leaflets upstream past a region in which the leaflets properly align and coapt to close the valve. A construction of fibrous tissue in the leaflets of the pulmonary and aortic valves operates to prevent prolapse of the leaflets in the pulmonary and aortic valves. A configuration of cord-like tendons, referred to as chordae tendineae, connected to muscular protrusions, referred to as papillary muscles, that project from the left ventricle wall tie the leaflets of the mitral valve to the walls of the left ventricle. The chordate tendinea provide dynamic anchoring of the mitral valve leaflets to the left ventricle wall that operate to limit upstream motion of the leaflets and prevent their prolapse into the left atrium during systole. Similarly, a configuration of chordae tendineae and papillary muscles cooperate to prevent prolapse of the tricuspid valve leaflets into the right atrium.
Efficient cardiac valve function can be complex and a cardiac valve may become compromised by disease or injury to an extent that warrants surgical intervention to effect its repair or replacement. For example, normal mitral valve opening and closing and prevention of regurgitation of blood from the left ventricle into the left atrium is dependent on coordinated temporal cooperation of the mitral leaflets, the mitral annulus, the chordae, papillary muscles, left ventricle, and left atrium. Malfunction of any of these components of a person's heart may lead to mitral valve dysfunction and regurgitation that warrants surgical intervention to provide the person with an acceptable state of health and quality of life.